The present invention relates to a device for extraction of greases in aerosol form from an air flow in a ventilation system, which device comprises a number of intermediate plates which define both an increased surface of deposition for the greases, and an extended flow path in the ventilation system, which flow path exhibits an alternating direction of flow and an alternating cross sectional area.
In ventilation ducts from kitchens, especially restaurant kitchens such as hamburger bars and the like, greases in aerosol form (xe2x80x9csmell of fryingxe2x80x9d) accompanying the exhaust air from frying-hearths and deep-frying pans e.g., are deposited due to inadequate filtration in existing filters. The deposition of these greases takes place in the entire ventilation duct, all the way up to the fan housing, whereby it gives rise to a risk of extensive fire in the entire duct. Due to this, ventilation ducts in restaurant kitchens must today be cleansed at short intervals and at very high costs, in order to prevent incrustation among other things and to prevent major damage caused by fires.
Various devices intended to diminish or eliminate problems with depositions of greases in ventilation ducts, are previously known. In GB 1,491,672 e.g., a static impeller is presented, which is intended to give rise to a rotation in the air flow through the duct, in order to centrifuge particles of grease towards the walls and allowing them to flow down along the same. The intended effect of the impeller ought however be marginal, since only a minor rotation can be accomplished by a static impeller. The same problem ought to arise in connection with the device shown in WO 96/11047, which also comprises a static impeller intended to give rise to a rotation in a gas flow.
In U.S. Pat. No. 4,607,614, an especially designed hood for a ventilation system is presented, which exhibits plates that deflect the air flow in alternating directions for the creation of a turbulent flow with velocity changes. The air flow is moreover distributed over the width of a special grease collecting arrangement, over a number of ducts having baffles that create a rotating flow in the same. Spray nozzles are arranged to spray water through the air flow in order to achieve a scrubber effect and the resulting grease-mixed water is drained off through an outlet arranged at the lower end of the hood. Even if the device shown in U.S. Pat. No. 4,607,614 ought to have a good degreasing effect, it is far too complicated and thereby inevitably expensive, for it to be used in any greater extension.
This is especially the case since the restaurant in question must exchange the entire of their existing hoods for the especially designed hood according to U.S. Pat. No. 4,607,614.
U.S. Pat. No. 3,870,494 is showing an insert for a ventilation hood. The insert exhibits a number of parallel flow paths between a number of inlets 30 and a number of outlets 31. In each flow path, the air flow only passes two inclined intermediate plates, namely the plates 36 and 37. It is stated to be important to keep the pressure drop low, which is the reason for the large inlet and outlet openings and the low number of intermediate plates.
U.S. Pat. No. 3,813,856 is showing an insert very much alike the one shown in U.S. Pat. No. 3,870,494, with the exception that the intermediate plates are not inclined.
U.S. Pat. No. 4,266,529 is showing an insert where three inclined walls 40, 41, 45 are consecutively arranged in a ventilation hood, see FIG. 4. The intermediate plates exhibit a free, bent edge 42 which is placed at the lowermost point or line in the purpose of catching and diverting caught grease.
GB 1,566,718 is not related to a grease trap for a ventilation system, but is related to a free standing device for the removal of washing liquid remaining in a gas flow after a scrubber for the gas flow. In the introduction of the document, there is a discussion of the problems that are considered to arise in connection with the use of planar, possibly inclined intermediate plates. The solution to these problems is, according to the document, the use of curved intermediate plates, which are arranged to define a sinusoidal flow path for the gas flow. Hereby, there is achieved a centrifugation effect which brings liquid in the gas flow to deposit on the curved intermediate plates, to form a liquid flow on the same. When this liquid flow reaches a flange 26, 28 at an upper, free edge of the intermediate plate, the liquid is caught by the flange and falls directly down into a collecting reservoir.
Accordingly, there is a need today for a relatively simple and thereby relatively cheap, passively operating and thereby reliable in operation, grease trap which may be mounted in existing ventilation ducts in a simple way.
The present invention aims at presenting a device for the trapping of greases in aerosol form from an air flow in a ventilation duct, which device eliminates or at least diminishes the problems mentioned above. The invention aims especially at presenting such a device which, despite the fact that it is of relatively simple design, exhibits increased surfaces for deposition of the greases and an extended flow path in the ventilation system, which flow path exhibits an alternating direction of flow and an alternating cross sectional area, whereby a turbulent air flow of varying direction and varying velocity is achieved. Hereby, the agglomeration of grease particles and the deposition of the same on the deposition surfaces, is favoured. Furthermore, the invention aims at presenting such a device which is self-rinsing, thanks to all main deposition surfaces sloping towards an outlet in a lowermost point of the device. It is also an object of the invention to present such a device which may be mounted in an existing ventilation duct, e.g. directly above a ventilation hood, but upstream an air flow inducing device, i.e. a fan.
These and other objects are achieved by the device according to the invention, such as presented in the claims.
The fundamental principle behind the function of the device is that an increased cross sectional area and an extended flow path for the air flow is achieved in a given room, i.e. a given section of a ventilation duct, the cross-sectional area preferably being at least 100% larger than the cross-sectional area of the existing ventilation duct, at the same time as increased deposition surfaces and a flow path that constantly changes direction, is achieved. Moreover, the cross-sectional area in the thus created, extended flow path varies all the time, which means that the air will be forced to flow alternatingly with a high velocity, in order to then abruptly turn into a very low velocity. Together with turbulence creating means, this leads to beneficial conditions for the grease particles to merge and then to fall down on the deposition surfaces when the air velocity decreases.